1. Field of the Invention
The present invention relates to a foam member having shape memory property. Especially, the present invention relates to a foam member used for fluid sealing, soundproofing, and thermal insulation and to a method of producing the same.
Further, the present invention relates to an engine noise-proof cover for the purpose of reducing noise made by a car engine.
2. Description of the Related Art
Various kinds of foam materials such as a urethane foam and silicon sealants such as liquid hardening sealant are widely used for fluid sealing, soundproofing, and thermal insulation in joints of buildings, industrial machinery, and automobiles. In order to obtain enough performances of fluid sealing, soundproofing, and thermal insulation, gaps between joints of structures need to be filled up with theses materials.
A conventional foam member are attached on a portion where a process such as fluid sealing, soundproofing, and thermal insulation is necessary (hereinafter, referred as a xe2x80x9cprocessed portionxe2x80x9d) in a compressed state, and the foam member fills gaps between joints by recovering the thickness with an elastic force of the foam member itself. However, since the conventional foam member recovers its original shape as soon as a pressure thereon is released, the foam member or an assembly using the foam member need to be attached on the processed portion with keeping the foam member compressed against its recovery force. Therefore, operatability of attachment is very low.
If the foam member is thin, the operatability of attachment is improved. However, the performances of fluid sealing, soundproofing, and thermal insulation becomes insufficient since gaps are generated between the structure and the foam member in the processed portion. Alternatively, the recovery force of the foam member at the compressed state can be decreased by using a soft foam member, but its effect is slight. On the contrary, since use of the soft foam member results in lowering strength of the foam member, a life of the foam member is shortened. Especially, the performance of fluid sealing becomes inferior. As discussed above, each performance of fluid sealing, soundproofing, and thermal insulation and the operatability of attachment were hardly accomplished at the same time. Therefore, a foam member satisfying each performance at the same time is demanded.
On the other hand, a sealant of liquid hardening type such as a silicon sealant is also used. In the case of such a sealant, a material in liquid form is poured into gaps of the processed portion, and the gaps are filled by hardening the material with a chemical reaction or volatility of a volatile material such as a solvent. However, the sealant of liquid hardening type necessitates a long time for a sealing operation, and it takes a long time for hardening the material itself.
According to Japanese published examined patent application Sho. 48-1903, an elastic synthetic resin impregnated with a viscous resin composite is compressed, and the resin is restored with using hysteresis of time-recovery in order to fill a gap. However, since this method necessitates a complicated process such as impregnation of a viscous resin composite, the cost becomes high.
According to Japanese published unexamined patent applications Hei. 10-110059 and 9-132668, a shape-recovery foam element consisting of a closed-cell resin foam element is disclosed. However, there is a problem that enough performances of fluid sealing, soundproofing, and thermal insulation cannot be obtained immediately since this foam element necessitates a long time, e.g. dozens of days, for recovering the original shape.
Japanese published examined patent application Hei. 7-39506 (JP-B-7-39506) discloses a shape-memory polymer foam element made of urethane, and Japanese published unexamined patent application Hei. 9-309986 (JP-A-9-309986) discloses a shape-memory vulcanized rubber molding in which rubber is blended with resin. Further, it is known that polynorborenene and styrene-butadiene copolymer can be made as a shape memory polymer; therefore, a foam element having a shape recovery characteristic can be obtained with these materials. However, in order to produce the foam element with a shape recovery characteristic, some specific materials, which is difficult to obtain, are necessary, and special producing plants are also necessary. Therefore, this kind of foam elements is not widely used.
Hereinafter, a conventional engine soundproof cover is discussed in detail.
In order to prevent noise generated from a car engine, the engine is usually covered with an engine soundproof cover. For example, FIG. 1 is a perspective view showing an engine soundproof cover 10 for use in a V-type engine 20. The engine soundproof cover 10 is formed so that a foam member 12 is provided as a soundproof member substantially all over the engine-side surface (inner surface) of a cover body 11 made of metal or resin. The engine soundproof cover 10 is fixed to fastening holes 15 provided in an intake manifold 13, an intake collector 14, and the like, by bolts (not shown).
In addition, the shape of the engine 20 is complicated. Accordingly, the engine soundproof cover 10 is attached to the engine 20 in the state where the foam member 12 is compressed in the direction of its thickness. Then, the thickness of the foam member 12 is recovered by an elastic force of the foam member 12 itself so as to fill up a gap between the cover body 11 and the engine 20. Thus, the soundproof effect is enhanced. However, usually, the foam member 12 recovers its thickness immediately as soon as the pressure is released. It is therefore necessary to attach the engine-proof cover 10 to the engine 20 while keeping the compressed foam member 12 in the compressed state against the recovery force of the foam member 12. Thus, the operatability of attachment is very low.
If the foam member 12 is made thin, the workability on attachment is improved. However, there appears a gap between the foam member 12 and the engine 20 so that the soundproof performance becomes insufficient. Although the recovery force from the compressed state can be lowered by use of a soft foam member 12, the effect is slight. If anything, reduction in the strength of the foam member 12 caused thereby leads to a problem such as shortening of the life.
Although it is also considered to mold the foam member 12 in accordance with the shape of the engine 20, it is necessary to prepare the foam member 12 for every kind of engine 20 and for every attachment place if such foam members 12 are attached to a plurality of places of the engine 20. Thus, the product cost is increased. In addition, because the foam member 20 is not brought into pressure contact with the engine 20, it is inevitable to generate a gap, though it is small, between the foam member 12 and the engine 20. Thus, there is a problem also in the point of view of the soundproof performance.
In view of the above circumstances, a first object of the present invention is to provide a foam member which is excellent in performances of fluid sealing, soundproofing, and thermal insulation, is excellent in the operatability of attachment to the processed portion, and is obtained at low cost without requiring a special material and equipment for producing.
Further, as discussed above, since the operatability of attachment of the engine soundproof cover to the engine is incompatible with the soundproof performance thereof. It is therefore a second object of the present invention to provide an engine soundproof cover which is excellent both in operatability of attachment and soundproof performance.
The inventors of the present invention made diligent investigation to solve the foregoing problem. As a result, the present inventors reached the following discovery. If a shape recovery foam member of the present invention is treated with the specific process which does not require special equipment, that is, releasing pressure after cooling in the state where the foam member is compressed after heating and compressing, then the compressed shape of the foam member is retained in the state where an external force is not applied in the normal temperature, and the thickness of the foam member is recovered by heating. Each satisfactory performance of fluid sealing, soundproofing, and thermal insulation is obtained by using the above shape memory foam member in a processed portion, and an operation of attachment can be easily performed. The present invention is based on such knowledge.
In order to attain the above objects, a foam member of the present invention is characterized as follows. A foam member having a coefficient of water absorption in a range between 0.01 g/m3 and 0.2 g/m3 is heated and compressed. With keeping the compressed state, the foam member is cooled. Then, the foam member is obtained by releasing the pressure. The foam member substantially recovers its original shape, which is the shape before compression, by heating. Further, a method of producing a foam member of the present invention is characterized as follows. A foam member having a coefficient of water absorption in a range between 0.01 g/m3 and 0.2 g/m3 is heated and compressed. With keeping the compressed state, the foam member is cooled. Then, the shape in the compressed state is retained after releasing the pressure.
Further, the inventors of the present invention made diligent investigation to solve the foregoing problem. As a result, the present inventors reached the following discovery. That is, if a shape memory foam member kept to be compressed in its thickness direction was used for an engine soundproof cover, the operatability of attachment of the engine soundproof cover to an engine was improved conspicuously. Then, the compressed shape memory foam member recovered its approximately original shape (thickness) before compression by heating or occasionally by heat generated from idling of the engine. As a result, the gap between a cover body and the engine was filled up by the shape memory foam member so that satisfactory soundproof performance could be obtained. The present invention is based on such knowledge.
That is, in order to achieve the above object, according to the present invention, there is provided an engine soundproof cover disposed to cover an engine, characterized in that a shape memory foam member is provided on a surface of the soundproof cover which covers the engine. Particularly, the shape memory foam member is a foam member which is obtained by heating and compressing a foam member, cooling the compressed foam member while keeping a compressed state thereof, and releasing the pressure after cooling, and which recovers an approximately original shape before compression by heating.
Further, in order to achieve the same object, according to the present invention, there is provided an engine soundproof structure comprising a soundproof cover disposed to cover an engine, characterized in that a shape memory foam member is provided on a surface of the soundproof cover which covers the engine.